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The Role of Muscles

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  1. The Role of Muscles Applied Kinesiology 420:151

  2. Agenda • Introduction to muscles • Attachments • Structural classification • Types of muscle action • Factors affecting muscle function • Coordination of muscles • Types of movements

  3. Introduction to Muscles • Movement occurs via: • Internal force • External force. Examples?

  4. Introduction to Muscles • Properties of skeletal muscle: • Extensibility • 50% increase • Tendons too • Contractility • 50% decrease • Only muscle • Elasticity • Tendons too • Irritability

  5. Agenda • Introduction to muscles • Attachments • Structural classification • Types of muscle action • Factors affecting muscle function • Coordination of muscles • Types of movements

  6. Attachments • How does skeletal muscle attach to bones? • Directly? • Connective tissue coverings (tendon) • Tendons: • Round cord, flat band, aponeurosis • Embedded within bone

  7. Attachments • Origin and insertion • Tendon length • Stability/mobility tendency • Proximal/distal tendency • Proximal and distal attachment • Less error • Example (arm curl vs chin-up)

  8. Attachments • More terms • Extremities: Proximal and distal • Diaphragm: Peripheral and central • Head/Neck/Trunk: • Vertical lines of pull: Upper and lower • Horizontal lines of pull: Medial and lateral

  9. Agenda • Introduction to muscles • Attachments • Structural classification • Types of muscle action • Factors affecting muscle function • Coordination of muscles • Types of movements

  10. Structural Classification • Fiber arrangement • Longitudinal • Quadrate • Triangular (radiate) • Fusiform • Unipenniform • Bipenniform • Multipenniform

  11. Longitudinal • Structure: • Long • Strap-like • Consistent diameter • Examples: • Sartorius • Rectus abdominis Figure 8.7

  12. Quadrate • Structure: • Four-sided • Usually flat • Examples: • Pronator quadratus • Rhomboid Figure 3.3

  13. Triangular (Radiate) • Structure: • Fibers radiate from narrow to broad attachment • Examples: • Pectoralis major • Gluteus medius Figure 3.3

  14. Fusiform • Structure: • Rounded • Tapered endings • Examples: • Biceps brachii • Brachialis Figure 3.3

  15. Unipenniform • Pennate  Feather • Structure: • Series of short parallel fibers • Feather-like arrangement from side of tendon • Examples: • Extensor digitorum longus • Tibialis posterior Figure 3.3

  16. Bipenniform • Structure: • Similar to unipenniform • Two sets of fibers • Examples: • Flexor hallucis • Rectus femoris Figure 3.3

  17. Multipenniform • Structure: • Similar to bipenniform • Multiple tendons • Examples: • Middle deltoid Marieb & Mallet, 2001, Figure 11.3

  18. Effect of Fiber Arrangement on Force Output • Concept #1: Force directly related to cross-sectional area  more fibers • Example: Thick vs. thin longitudinal/fusiform muscle? • Example: Thick fusiform/longitudinal vs. thick bipenniform muscle? • Concept #2: As degree of pennation increases, so does # of fibers per CSA

  19. Agenda • Introduction to muscles • Attachments • Structural classification • Types of muscle action • Factors affecting muscle function • Coordination of muscles • Types of movements

  20. Types of Muscle Action • Contraction vs. action • Concentric • Internal > external = + work • Eccentric • External > internal = - work • Isometric • Internal = external = 0 work • Isotonic • Is this really possible? • Isokinetic

  21. Agenda • Introduction to muscles • Attachments • Structural classification • Types of muscle action • Factors affecting muscle function • Coordination of muscles • Types of movements

  22. Factors Affecting Muscle Function • Line of pull • Angle of attachment • Length-tension relationship • Force-velocity relationship • Stored elastic capabilities

  23. Line of Pull • The direction of any movement caused by a muscle is due to: • #1: Joint structure • Example: Elbow flexion (biceps brachii) vs. knee extension (rectus femoris) • #2: The relation of the line of pull to the joint • Example: Upper fibers pectoralis major as abductor/adductor

  24. The location of the line of pull in relation to the joint center determines the movement in this case Figure 3.4

  25. Angle of Attachment • The angle of attachment affects the efficiency of the movement • Internal forces have two components • Rotary force • Parallel force • Stabilizing • Dislocating Parallel forces do not cause movement therefore reduce efficiency

  26. Perpendicular No Parallel Force Stabilizing or dislocating? Maximum efficiency Hamill & Knutzen, 2004, Figure 3.23

  27. Stabilizing or dislocating? More or less? Hamill & Knutzen, 2004, Figure 3.23

  28. Length-Tension Relationship • Optimal length rule  Slightly longer than maximum resting length • Too short  no force  why? • Too long  no force  why?

  29. Active + Passive Optimal? Active Too long? Too short? Passive Figure 3.7

  30. Force-Velocity Relationship • Concentric actions • Inversely related • Vmax = F0  vice-versa • Why? Cross-bridges take time • Eccentric actions • Directly related until . . .

  31. Figure 3.8

  32. Stored Elastic Capabilities • Rapid stretch  concentric action = more work • Why? Stored elastic energy • As speed increases so does effect • Up to a certain point • Addition of stretch reflex  SSC

  33. Agenda • Introduction to muscles • Attachments • Structural classification • Types of muscle action • Factors affecting muscle function • Coordination of muscles • Types of movements

  34. Coordination of Muscles • Role of muscles • Biarticular muscles

  35. Role of Muscles • Agonists • Directly responsible for movement • Synergists • Stabilizers • Neutralizers • Antagonists • Reciprocal inhibition • Braking

  36. Synergists as Stabilizers Support of limb  Deltoid example Figure 3.9

  37. Synergists as Neutralizers Pectoralis minor and serratus anterior

  38. Biarticular Muscles • Proximal/distal attachments cross 2 joints • Not long enough for full ROM • Result? Tension of one biarticular muscle transferred to opposite muscle • Example: Hamstrings and rectus femoris • Advantage over monoarticular muscles? Concurrent Movement

  39. Biarticular Muscles • Concurrent vs. countercurrent movements • Maximum ROM • Passive/active insufficiency

  40. Agenda • Introduction to muscles • Attachments • Structural classification • Types of muscle action • Factors affecting muscle function • Coordination of muscles • Types of movements

  41. Types of Movements • Passive • Example: Partner stretch or falling to ground • Active: • Slow  Constant force = inefficient • Rapid  Ballistic = efficient • How to stop ballistic movement • Antagonist • Passive resistance of connective tissue and eccentric action • External object

  42. Review • The muscle fiber (pp. 46-48) • Fast vs. slow twitch (pp. 48)